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Host immune responses must be tightly regulated by an intricate balance between positive and negative signals while fighting pathogens; persistent pathogens may usurp these regulatory mechanisms to dampen host immunity to facilitate survival in vivo. Here we report that Tim-3, a negative signalling molecule expressed on monocytes and T cells, is up-regulated on natural killer ( NK) cells in individuals chronically infected with hepatitis C virus ( HCV). Additionally, the transcription factor T-bet was also found to be up-regulated and associated with Tim-3 expression in NK cells during chronic HCV infection. Micro RNA-155 (mi R-155), an mi RNA that inhibits signalling proteins involved in immune responses, was down-regulated in NK cells by HCV infection. This Tim-3/ T-bet over-expression and mi R-155 inhibition were recapitulated in vitro by incubating primary NK cells or NK92 cell line with Huh-7 hepatocytes expressing HCV. Reconstitution of mi R-155 in NK cells from HCV-infected patients led to a decrease in T-bet/ Tim-3 expression and an increase in interferon- γ production. Blocking Tim-3 signalling also enhanced interferon- γ production in NK cells by improving signal transducer and activator of transcription-5 phosphorylation. These data indicate that HCV-induced, mi R-155-regulated Tim-3 expression regulates NK cell function, suggesting a novel mechanism for balancing immune clearance and immune injury during chronic viral infection. [ABSTRACT FROM AUTHOR]

In this study, we engineered Listeria monocytogens (Lm) by deleting the LmΔactA/ΔinlB virulence determinants and inserting HCV-NS5B consensus antigens to develop a therapeutic vaccine against hepatitis C virus (HCV) infection. We tested this recombinant Lm-HCV vaccine in triggering of innate and adaptive immune responses in vitro using immune cells from HCV-infected and uninfected individuals. This live-attenuated Lm-HCV vaccine could naturally infect human dendritic cells (DC), thereby driving DC maturation and antigen presentation, producing Th1 cytokines, and triggering CTL responses in uninfected individuals. However, vaccine responses were diminished when using DC and T cells derived from chronically HCV-infected individuals, who express higher levels of inhibitory molecule Tim-3 on immune cells. Notably, blocking Tim-3 signaling significantly improved the innate and adaptive immune responses in chronically HCV-infected patients, indicating that novel strategies to enhance the potential of antigen presentation and cellular responses are essential for developing an effective therapeutic vaccine against HCV infection. [ABSTRACT FROM AUTHOR]

Human monocytes/macrophages (M/MФ) of the innate immunity sense and respond to microbial products via specific receptor coupling with stimulatory (such as TLR) and inhibitory (such as Tim-3) receptors. Current models imply that Tim-3 expression on M/MØ can deliver negative signaling to TLR-mediated IL-12 expression through trans association with its ligand Galectin-9 (Gal-9) presented by other cells. However, Gal-9 is also expressed within M/MØ, and the effect of intracellular Gal-9 on Tim-3 activities and inflammatory responses in the same M/MØ remains unknown. In this study, our data suggest that Tim-3 and IL-12/IL-23 gene transcriptions are regulated by enhanced or silenced Gal-9 expression within monocytes through synergizing with TLR signaling. Additionally, TLR activation facilitates Gal-9/Tim-3 cis association within the same M/MØ to differentially regulate IL-12/IL-23 expressions through STAT-3 phosphorylation. These results reveal a ligand (Gal-9) compartment-dependent regulatory effect on receptor (Tim-3) activities and inflammatory responses via TLR pathways—a novel mechanism underlying cellular responses to external or internal cues. [ABSTRACT FROM AUTHOR]

Highlights: [•] We explore the mechanisms underlying vaccine failure in hepatitis C-infected subjects. [•] Hepatitis B vaccine failure was associated with up-regulation of Tim-3 on monocytes. [•] Vaccine failure was associated with dysregulated IL-12/23 expressions in monocytes. [•] Vaccine failure was also associated with TH17 cell accumulation. [•] Ex vivo Tim-3 blockade corrected the imbalance of IL-12/IL-23/TH17. [ABSTRACT FROM AUTHOR]

Coinfection of hepatitis B virus (HBV) with hepatitis C virus (HCV) is quite common, leading to an increase in morbidity and mortality. As such, HBV vaccination is recommended in HCV-infected individuals. However, HBV vaccine responses in HCV-infected individuals are often blunted compared with uninfected populations. The mechanism for this failure of vaccine response in HCV-infected subjects remains unclear. In this study, we investigated the expression and function of an inhibitory receptor, killer cell lectin-like receptor subfamily G member 1 (KLRG1), in the regulation of CD4+ T cells and HBV vaccine responses during HCV infection. We demonstrated that KLRG1 was overexpressed on CD4+ T cells from HCV-infected, HBV vaccine nonresponders compared with HBV vaccine responders. The capacity of CD4+ T cells to proliferate and secrete IL-2 cytokine was inversely associated with the level of KLRG1 expression. Importantly, blocking KLRG1 signaling resulted in a significant improvement in CD4+ T cell proliferation and IL-2 production in HCV-infected, HBV vaccine nonresponders in response to TCR stimulation. Moreover, blockade of KLRG1 increased the phosphorylation of Akt (Ser473) and decreased the expression of cell cycle inhibitors p16ink4a and p27kip1, which subsequently enhanced the expression of cyclin-dependent kinase 2 and cyclin E. These results suggest that the KLRG1 pathway impairs CD4+ T cell responses to neoantigen and induces a state of immune senescence in individuals with HCV infection, raising the possibility that blocking this negative-signaling pathway might improve HBV vaccine responses in the setting of chronic viral infection. [ABSTRACT FROM AUTHOR]